The proposed research builds on data from a long-term study of the population dynamics of
mountain yellow-legged frogs (Rana sierrae and Rana muscosa) in the California Sierra Nevada
mountains, and the impacts of the amphibian chytrid fungus, Batrachochytrium dendrobatidis
(= Bd), as it has invaded and spread through frog populations in hundreds of high elevation
lakes. In most cases, invasion of Bd results in epizootics of the disease chytridiomycosis,
rapid frog population declines, and local extinctions, but in some cases long-term persistence
of frog populations occurs with Bd in an enzootic state. The proposed research will investigate
the patterns of change in both the frog and the fungus as Bd swept across the Sierra Nevada,
and the implications of these changes for Bd virulence and frog resistance/tolerance to infection.
This will be accomplished through a combination of cutting-edge genomic analysis of skin swab
samples, surveys of field populations, collection of Bd cultures and frog mucosal samples
from field populations, and laboratory experimentation on Bd virulence and frog susceptibility.
Intellectual Merit :
Outbreaks of emerging infectious diseases are increasingly recognized as major threats to
wildlife populations, with important implications for species conservation. The initial invasion
of a novel pathogen into susceptible host populations often results in epizootics characterized
by high host mortality and population declines, during which time strong selection can occur
on both the host and pathogen. Chytridiomycosis has had catastrophic effects on amphibians
worldwide, with numerous species extinctions documented in recent decades and many more at
risk of Bd-caused declines. The proposed research will contribute to the understanding of
the role of infectious diseases, such as chytridiomycosis, as agents of evolutionary change
in natural populations. The research will make use of recent advances in molecular approaches,
and the extensive dataset and archive of samples from the R. sierrae/R. muscosa-Bd system,
to investigate how both host and pathogen populations change during the transition from pre-pathogen
arrival, to disease epizootic, to enzootic disease, to potential recovery of the pre-disease
host population abundances. This dataset will be used to investigate the genetic basis for
differences in host resistance/tolerance and pathogen virulence.
Broader Impacts :
This proposed research has general implications for the conservation and long-term survival
of wildlife species threatened by emerging infectious diseases, with specific relevance for
R. sierrae/R. muscosa. Because of the severity of the declines experienced by these species,
they are currently the focus of intense multi-agency conservation efforts. As such, the proposed
study presents an unusual opportunity to conduct research that could provide crucial guidance
to efforts aimed at reversing the decline of these species, including re-establishing R. sierrae/R.
muscosa in Bd positive areas from which they were previously extirpated by Bd epizootics.
The results will be disseminated broadly through presentations at national and international
conferences, social media, open access publications, and publically available data archives.
The research program will contribute to undergraduate education at UCSB and UC Berkeley, through
integration with undergraduate general education courses in disease ecology and global change
biology (reaching ~350 students per year). Undergraduate and graduate students from diverse
backgrounds will be recruited to participate in both field and laboratory studies related
to the proposed project. The considerable public visibility of, and interest in, amphibian
declines will provide opportunities to develop public outreach activities, including presentations
to conservation organizations and K-12 schools.